1. Field of the Invention
The present invention relates to a keyboard to be used as an input device for word processors and personal computers.
2. Description of Related Art
A keyswitch assembly for use on such a keyboard typically has a key provided with a stem projecting from the lower surface thereof, and a key guide member formed on a base plate and provided with a guide hole receiving the stem of the key to guide the key for vertical movement.
It is desirable that the stroke of fingers is as small as possible to enable fast key operation. Keyboards of the so-called slope-sculptured type are proposed in U.S. Pat. Nos. 4,560,845 and 4,735,520. In these keyboards, the upper surfaces of the keys are formed in curved surfaces suitable for operation with fingers to improve the operability of the keys, and the keys are arranged, from the view point of human engineering, so that a downward convex envelope is tangential to the upper surfaces thereof to reduce the fatigue of the operator in operating the keys.
In such a previously proposed keyboard, it is preferable that the keys move respectively along normals to the envelope, and hence the key guide members must be arranged on a downward convex curved surface.
However, in a keyboard provided with keyswitch assemblies each having a key provided with a stem and key guide members formed on a base plate, each key guide member having a guide hole receiving the stem of the key to guide the key for vertical movement, the key is liable to tilt relative to the guide hole. Consequently, the stem of the key moves awkwardly. When the length of the key guide member is reduced to increase the stroke of the key, the key is unable to move smoothly. Therefore, the key guide member must be sufficiently long, which is an impediment to the reduction of the thickness of the keyboard.
When such keyswitch assemblies provided with the key having the stem are applied to a keyboard of a slope-sculptured type, the key guide members must be formed having a tubular shape so as to extend respectively in different directions. Accordingly, a plurality of slide dies must be used in forming the base plate by molding a resin. Alternatively, a base plate formed in a flat shape by molding must be curved by an additional shaping process, which increases the manufacturing cost of the keyboard.